In the related art, a coordinate input device, which detects the position of an indication tool (for example, a pen) operated in a predetermined coordinate input region, is known. A coordinate input device, which forms a light (infrared light) layer along a display surface on the display surface on which an image is displayed, and detects the indication positions of the indication tool by detecting the positions of light reflected by the indication tool when a predetermined position on the display surface is indicated by the indication tool, is known as an example of such a coordinate input device (for example, refer to PTL 1).
The coordinate input device disclosed in PTL 1 includes an effective coordinate input region forming the display surface of a display device; multiple sensor units including a light projection unit forming the light layer along the coordinate input region, and a light receiving unit; retroreflective units which are respectively disposed on three outer sides of the effective coordinate input region, and reflect incident light; and a control/computational unit. In the coordinate input device, the multiple sensor units detect the change range of a light quantity distribution caused by the operation of the indication tool in the effective coordinate input region, and the control/computational unit calculates a coordinate value in the effective coordinate input region based on the number of change ranges and the number of pen-downs of the indication tool.
In such a coordinate input device, the light projection unit of the sensor unit includes an infrared light emitting diode (LED) emitting infrared light, and a projection lens projecting the infrared light in a range of approximately 90°. The light projection unit is fixed to an upper hood.